Recurrent word
In mathematics, a recurrent word or sequence is an infinite word over a finite alphabet in which every factor occurs infinitely often. An infinite word is recurrent if and only if it is a sesquipower.
A uniformly recurrent word is a recurrent word in which for any given factor X in the sequence, there is some length nX (often much longer than the length of X) such that X appears in every block of length n: the term minimal sequence or almost periodic sequence(Muchnik, Semenov, Ushakov 2003) is also used.